1. Field of the Invention
The present invention relates generally to optical communications, and more specifically to optical fibers having low bending loss suitable for splicing and for the fabrication of optical fiber components.
2. Technical Background
A high performance optical telecommunication system carries high data rates over long distances with no electronic regeneration. For example, rates of 10 Gb/s or more over unregenerated distances of three to five hundred kilometers have been achieved. A high performance system may employ high power signal lasers, optical amplifiers, dispersion compensation devices, optical switching devices, and may use wavelength division multiplexing. Optical telecommunications systems are progressing toward higher speeds and longer span lengths, making the requirements for system components more and more arduous.
One such system component is an optical fiber coupler. Optical fiber couplers provide for coupling of optical signals between optical fibers, and are ubiquitous in the devices used in optical telecommunications systems. Optical fiber couplers may be made, for example, by heating and stretching a pair of coextending optical fibers to fuse and taper them. An optical signal traveling in one of the optical fibers is evanescently coupled into the other optical fiber in the fused region. Optical fiber couplers are used in a variety of devices to split and combine optical signals. For example, optical coupler may be used to divide optical power between two paths with a desired ratio (e.g. 1:1, 9:1). An optical fiber coupler may also be used as a WDM to combine pump radiation with an optical signal in an erbium-doped fiber amplifier.
As the requirements for the optical performance of optical fiber couplers become ever more stringent, the need to eliminate sources of loss becomes critical. One such loss source is bending loss in the unfused regions of the optical fibers. Optical fiber couplers are generally made to have relatively long (e.g. 2-5 m) lengths of optical fiber leading from the coupling region. When an optical fiber coupler is assembled in a device, these optical fiber leads are often bent with a small radius or coiled around a spool. Conventional fibers used in the manufacture of optical fiber couplers tend to have relatively high bend losses, giving the assembled device an unacceptably high loss. While the use of conventional low-bend loss optical fibers will reduce bending losses, couplers fabricated from such fibers tend to exhibit high coupling losses. Further, splices between the low bend-loss optical fiber leads and other device components, such as erbium-doped optical fiber, tend to have relatively high losses.
Conventional optical fibers do not provide for the manufacture of optical fiber couplers with the desired performance. There remains a need for an optical fiber that exhibits low bending loss while also having low splice loss, low attenuation, and the ability to be fabricated into a low-loss optical fiber coupler. From the cost and process point of view, ease of manufacture and insensitivity of optical fiber properties to process variations are also highly desirable properties.
The following definitions are in accord with common usage in the art.
The refractive index profile is the relationship between refractive index and optical fiber radius.
Delta, xcex94, is the relative refractive index percent, xcex94=(n12xe2x88x92nc2)/2nc2, where n1 is the specified refractive index in region i, and nc is the average refractive index of the cladding region.
The term xcex1-profile refers to a refractive index profile, expressed in terms of xcex94(b), where b is radius, which follows the equation
xcex94(b)=xcex94(b0)(1xe2x88x92[|bxe2x88x92b0|/(b1xe2x88x92b0)]xcex1) 
where b0 is the point at which xcex94(b) is maximum, b1 is the point at which xcex94(b) % is zero, and b is in the range b1xe2x89xa6bxe2x89xa6bf, where delta is defined above, bi is the initial point of the xcex1-profile, bf is the final point of the xcex1-profile, and xcex1 is an exponent which is a real number. Deltas are conventionally expressed as percents.
One aspect of the present invention relates to an optical fiber for the propagation of an optical signal having a wavelength, the optical fiber including a core; and a cladding layer surrounding the core, wherein the optical fiber has a bending loss of less than 0.5 dB at 1560 nm when wrapped 5 turns around a 20 mm mandrel; and an average fiber pull test loss of less than 0.1 dB in the wavelength range of 1530 nm to 1550 nm.
One aspect of the present invention relates to an optical fiber for the propagation of an optical signal having a wavelength, the optical fiber having a centerline, the optical fiber including a core surrounded by a cladding layer, the cladding layer having an outer radius rc and an average refractive index nc, the core including a central region disposed around the centerline of the fiber, the central region having a radius r1, a maximum delta xcex941 of between about 0.4% and about 1.5%, a refractive index profile, a maximum germania concentration [GeO2]1 of between about 8 wt % and about 30 wt %, and a germania concentration profile; and an annular region surrounding the central region, the annular region being surrounded by the cladding layer, the annular region having an outer radius r2, a minimum delta xcex942 of between about xe2x88x920.1% and about 0.05%, a refractive index profile, a maximum germania concentration [GeO2]2 of between about 2 wt % and about 22 wt %, a germania concentration profile, a maximum fluorine concentration [F]2 of between about 0.5 wt % and about 3.5 wt %, and a fluorine concentration profile.
Another aspect of the present invention relates to an optical fiber for the propagation of an optical signal having a wavelength, the optical fiber including a core surrounded by a cladding layer, the cladding layer having an average refractive index nc, the core including a central region having a radius r1, a maximum delta xcex941 of between about 0.4% and about 1.5%, a refractive index xcex1-profile having an xcex1 of between about 1 and about 10, a maximum germania concentration [GeO2]1 of between about 8 wt % and about 30 wt %, and a germania concentration profile; and an annular region, the annular region having a maximum germania concentration [GeO2]2 of between about 2 wt % and about 22 wt %, and a maximum fluorine concentration [F]2 of between about 0.5 wt % and about 3.5 wt %, the annular region having an inner subregion and an outer subregion, the inner subregion surrounding the central region, the inner subregion having a radius r2a, a maximum delta xcex942a of between about 0% and about 0.2%, a refractive index xcex1-profile having an xcex1 of between about 1 and about 10, the outer subregion surrounding the inner subregion and being surrounded by the cladding layer, the annular region having a radius r2b, a minimum delta xcex942b of between about xe2x88x920.1% and about 0%, and a refractive index profile.
Another aspect of the present invention relates to an optical fiber for the propagation of an optical signal having a wavelength, the optical fiber including a core surrounded by a cladding layer, the cladding layer having an average refractive index nc, the core including a central region having a radius r1, a maximum delta xcex941 of between about 0.7% and about 1.2%, a refractive index xcex1-profile having an xcex1 of between about 1 and about 10, a maximum germania concentration [GeO2]1 of between about 14 wt % and about 24 wt %, and a germania concentration profile; and an annular region, the annular region having a maximum germania concentration [GeO2]2 of between about 3.5 wt % and about 12 wt %, and a maximum fluorine concentration [F]2 of between about 0.7 wt % and about 1.2 wt %, the annular region having an inner subregion and an outer subregion, the inner subregion surrounding the central region, the inner subregion having a radius r2a, a maximum delta xcex942a of between about 0% and about 0.2%, a refractive index xcex1-profile having an xcex1 of between about 1 and about 10, the outer subregion surrounding the inner subregion and being surrounded by the cladding layer, the annular region having a radius r2b, a minimum delta xcex942b of between about xe2x88x920.1% and about 0%, and a refractive index profile.
Another aspect of the invention relates to an optical fiber component including an optical fiber for the propagation of an optical signal having a wavelength, the optical fiber having a centerline, the optical fiber including a core; and a cladding layer surrounding the core, wherein the optical fiber has a bending loss of less than 0.5 dB at 1560 nm when wrapped 5 turns around a 20 mm mandrel; and an average fiber pull test loss of less than 0.1 dB in the wavelength range of 1530 nm to 1550 nm.
The optical fibers of the present invention result in a number of advantages over prior art optical fibers. For example, the optical fibers of the present invention have low bend losses, and are suitable for the production of optical fiber couplers with low coupling loss. The optical fibers of the present invention may be spliced to conventional optical fibers with low loss. The optical fibers of the present invention also have low attenuation. Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the invention as described in the written description and claims hereof, as well as in the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework to understanding the nature and character of the invention as it is claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings are not necessarily to scale. The drawings illustrate one or more embodiment(s) of the invention, and together with the description serve to explain the principles and operation of the invention.